The Callahan Tunnel, a key artery connecting downtown Boston to Logan International Airport, will be closed for about three months starting at the end of December, the Massachusetts Department of Transportation announced today.

The entrance to the tunnel (David L. Ryan/Globe File)

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The closure is part of a $34.9 million project to update the 52-year-old tunnel’s deck, curb line, and gutters, and replace the wall panels, MassDOT said. The wall panels were preemptively removed in December because of significant erosion to the panels’ anchor system.

“The Callahan has served motorists well since the day it opened in 1961 and was paired with the Sumner tunnel,” said Frank DePaola, highway administrator for the Massachusetts Department of Transportation, in a statement. “However, every aspect of the tunnel is in fair to poor condition, and the time has come to put the Callahan in shape to last another 50 years.”

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Motorists are expected to be detoured on to Routes 1, 2, and 3, as well as Interstates 93 and 95, and are urged to use public transit or alternate routes to reach Logan, MassDOT said.

In mid-December, a single wall panel fell during the evening rush hour. No one was injured, but officials removed three additional panels as a precaution, followed by another 120 panels. This January, crews removed all 2,800 panels in the tunnel.

At a press conference, DePaola said staff monitoring the quality of the tunnel had noticed a sharp uptick in problems. There were spots where the asphalt had broken through to the concrete underneath. And as recently as two weeks ago, he said, a manhole cover had completely fallen out of its slot and beneath the road, requiring the lane to be closed while the cover was replaced.

“We had seen an increase in the frequency of these types of incidents, and we knew we needed to do something as a permanent repair,” DePaola said.

Without an overhaul project, DePaola said, the tunnel would have only remained safe for one to two more years.

“Certainly closing a major feature like this tunnel is going to be an inconvenience,” he said. He advised commuters who usually use the tunnel to head to Logan to leave themselves extra time for the trip.

But there is a small silver lining to the tunnel closure: While the Callahan Tunnel remains shuttered to traffic, tolls will be waived at the I-90 turnaround at Allston/Brighton, allowing motorists in the Back Bay to use the Mass Pike to reach other routes to East Boston without paying extra.

“We will have a significant traffic diversion plan encouraging people to use alternate routes to get to the airport,” DePaola said.

In its contract with the construction company in charge of the project, MassDOT has stipulated that the company can earn or lose $71,000 for each day the project goes under or over its anticipated finish time.

After the tunnel reopens at the end of March, there will also be a series of overnight closures that will continue through the next four months while workers replace the panels in the tunnel.

DePaola said they have timed the project so that it would not overlap with the repainting of Tobin Bridge, which is taking place this summer and next summer, and requires partial lane closures on the bridge.

If the tunnel were not closed completely, he said, the repair project would take 18 months, and also would not be as durable. The project would also have cost more if the tunnel were left partially open, DePaola said.

“In the past ... it prolonged the pain, so to speak, for the motorists,” DePaola. “In this case, we decided it would be best for all to just get this work done in the shortest period possible.”